1. Field of the Description
The present invention relates, in general, to projecting or displaying video/animated or still three dimensional (3D) images, and, more particularly, to autostereoscopy methods and systems for providing glasses-free 3D using a one dimensional (1D) retroreflective screen.
2. Relevant Background
There are numerous entertainment and other settings where it is desirable to create unique visual displays to entertain and excite viewers. For example, theme or amusement parks may include rides or walk-through attractions where guests (or “viewers”) are entertained by a unique visual effect or illusion. Often, it is desirable to create a display with three dimensional (3D) images, and, even more desirable for many entertainment facility operators is to provide the 3D display without requiring the viewer to wear special headgear or glasses, e.g., using autostereoscopy or similar techniques.
In recent years, the incorporation of 3D stereoscopic projection and imagery into ride attractions has been rapidly increasing. However, many of these attractions require that the rider wear 3D glasses, which causes the ride operator to purchase and provide the glasses and also to gather, clean, and replenish the 3D glasses. Additionally, many riders find the glasses to be uncomfortable, and the one-size-fits-all models are often ill-fitting requiring ongoing adjustment or repositioning by the wearers especially after rapid or jerky vehicle movements in the ride.
With these problems in mind, operators of entertainment facilities recognize that the use of autostereoscopic projection or 3D without need for glasses would greatly enhance the sense of immersion and improve the rider experience as well as reducing problems with providing glasses or headgear. Unfortunately, it has proven difficult to provide autostereoscopic displays for a large number of viewers. The difficulty is in part due to the need to provide appropriate left and right eye views for many people over a large viewing area. A large number of views are used to provide deep images without ghost images and to allow the display system to be robust to user head motion.
One effective way to produce autostereoscopic imagery for each viewer is to provide two projectors, such as microprojectors, in close proximity to each viewer's eyes that project onto a retroreflective screen. The projectors project appropriate left and right eye images toward the retroreflective screen, and the retroreflective screen sends the light back toward the projectors and the nearby left and right eyes. In other words, a left eye projector is provided that provides left eye images and a right eye projector is provided that provides right eye images. Further, the conventional retroreflective screen sends the light back without diffusing the light, and slight imperfections in the retroreflected direction allow each eye of the viewer to view the bright retroreflected images of the projector it is closest to but not the images from the other projector (e.g., each eye only sees the left or right eye images). The retroreflected direction is accurate enough that the brightness drops significantly when the eye is not nearly collocated with one of the projectors.
Unfortunately, it has proven cumbersome to place a pair of projectors next to each viewer's head. For example, many display applications have to be suited to viewers of varying height, which would force a display operator to provide adjustment of the location of the two projectors to suit each and every viewer's height and head location in the ride or show setting. Additionally, the use of two projectors and a conventional retroreflective screen locks the viewer into a single viewing position and does not allow the viewer to move their head during the ride or show as their eyes and the projectors will quickly not be collocated ruining the 3D imagery.
In some rides or attractions, a 3D display is created by combining the use of a beamsplitter with a conventional retroreflective screen. Projectors project imagery on the rear surface of the beam splitter, and this light is reflected toward the retroreflective screen where it is reflected back to a viewer looking through a front surface of the beamsplitter. While providing a 3D display, the viewer is forced to look through a beamsplitter. To provide a wide angle view, either the beamsplitter is placed very close to the viewer or a large beamsplitter must be used. Such 3D displays have not provided a truly immersive experience as the use of the beamsplitter separates the viewer from the scene by enclosing them, for example, in a ride vehicle, which reminds them they are looking at a virtual scene. Typically, the projectors must also track the viewer's head movements, which can prove difficult or add complexity to a display system or ride.
One approach is to provide a 1D retroreflective screen that retroreflects horizontally but diffuses vertically so viewers anywhere in a vertical strip or below the projectors see stereoscopic images. Prior 1D retroreflective screens have been made by taking 2D retroreflective materials, i.e., either spheres or corner cubes, and converting them to a diffusive 1D retroreflective material by layering a lenticular or directionally preferring diffuser. The lenticular and retroreflective material are sometimes spaced apart. The 2D retroreflector, even with the vertical diffuser, preferentially reflects back to the projector away from the viewer's head. A vertical diffuser preferentially diffuses about the incoming angle of light, which is towards the projector. Therefore, the vertical diffusion adds a vertical view zone about the projector but not about an average person's head height. The vertical diffusion angle must be large enough so the half angle of diffusion is large enough to cover from the projector to the range of viewer head heights. As a result, large amounts of light are wasted, and, further, half of the light still diffuses above the projectors away from a viewer's head.
In these prior screens, the 2D retroreflective material is made up of microspheres or corner cubes. For the spheres, only a ring of light incident on the spheres is retroreflected through total internal reflection such that there is a missing cone of light in the middle of the sphere that is not retroreflected. Hence, there is light loss. The corner cube retroreflects a majority of the light, but the reflection is not through total internal reflection but, rather, is through a metallized reflector. As a result, there is still an amount of light loss although this configuration may be brighter than a microsphere 1D retroreflective screen. The 2D retroreflective material made with spheres can be made roll-to-roll, but it is not as bright as the corner cube material, which cannot be made roll-to-roll and is typically stamped and tiled, which leaves seams in the screen.
These prior screens often have a spacing gap (e.g., 10 to 30 mm) between the 2D retroreflector and the vertical diffuser, which leads to a thicker multipiece screen assembly. The spacing may be air or a material (such as plastic). If the gap or spacing is relatively thick plastic (e.g., greater than 10 mm), the screen likely will not be flexible. If it is an air gap, the screen also will typically not be made flexible so as to ensure that the air gap is consistent throughout the screen. Regardless, these prior screens typically included some set of frames and frame holders to maintain the gap between the 2D retroreflector and the film. In addition to problems with rigid or non-flexible screens, the imagery may be less sharp due to the inclusion of the gap, e.g., an air gap may produce some blur.
Hence, there remains a need for improved visual display techniques and systems for creating or projecting 3D images. Preferably, such an advanced 3D display system would provide a high-contrast 3D dimensional image without requiring a viewer to wear special head gear or glasses. Further, it may be preferable that the 3D display system not require adjustments to suit a viewer's height, e.g., any viewer in a particular seat or other viewing location may view the 3D images without regard to their height and vertical position of the viewer's eyes.